I have been a new ArcFM user for almost a year and half now after being of the shelf Esri (ArcInfo now ArcGIS) now that I am in an electric utility. I have not used NISC Mapswise - but even though you were looking for a comparison at least an opinion of ArcFM might help.
It is easy to start off by saying to do a needs assessment or some review of required functionality to help determine which product is better to suit your needs, but some pro/cons from what meets our needs I can share.
Summary:
Pro: analytical and editing features - huge time savers and helps enforce data integrity and quality. Vendor has made great strides in easier to manage IT issues. Biggest users: Engineering, dispatch and designers.
Con: Very sensitive to proper configuration and enterprise features require a similar infrastructure similar to ArcGIS
Details:
With any 3rd party add on to ArcGIS you will always have to be aware of version changes, upgrade paths, and other compatibility issues. In the current versions of ArcFM the vendor Schinder is aligning more with the patterns and standards Esri and other technology vendors are going. Patches instead of full uninstalls, and a desktop / server / mobile / cloud suite of solutions. So the con has been previous versions were difficult to manage but is better and continues to improve.
The power of ArcFM especially for an electric utility is the Feeder manager, AutoUpdaters and analysis (tracing) tools. So this is a very big Pro but has some cons. One con is if you want to get the tracing and isolation tools off the desktop you need the infrastructure of ArcGIS and ArcFM servers - costly but we've seen these tools as widgets in web apps (seen not used).
To realize the power of the features ArcFM really needs to be configured properly. This would require either a lot of in house planning and research or a consultant to assist. Potential con. A pro of the ArcFM configuration is if you have an existing GIS database there might be some conversion but the configuration will allow you to designate what attribute fields are expected (kva, feeder ID, etc) for a bulk of your data in place.
If you have other systems integrating with your GIS - such as a CMSS, EAM, or other enterprise or desktop system there are some considerations. ArcFM wrappers around ArcGIS and an enterprise database. There is an object reader that needs to be installed for other applications to read the database, a simple no option install. For systems that might write to the database directly or ArcGIS geoprocessing outside of the ArcFM user environment you have to be aware of AutoUpdaters that might not get triggered. For example an Autoupdater takes individual Kva of transformer banks in a related table, upon a trigger - create or update - it will aggregate and sum the Kva and write the new summed value into the parent feature class attribute. In our design of our Enterprise Asset Management system we were potentially going to use a GP script to update these records in a versioned environment and post to default - which would not trigger the required AutoUpdaters for data integrity. These are non-issues if you're not in an enterprise environment or do not have system integration issues.
Finally the tools themselves inside ArcMap are pro for some. Coming from years of standard ArcGIS I often go back between the ArcFM tool and the ArcGIS tool - for example the identify tool - the ArcFM version hides some ArcFM system fields (like a trace weight) and presents it in a different looking window. The attribute editor is slightly beefed up too. I have found that novice to new GIS editors and users tend to pick up the ArcFM tools faster but really develop only an understanding of the ArcFM tools and get tripped up if moving to standard ArcGIS. The session manager is a GUI tool that can easily manage a versioned editing workflow and has simple workflow (open, submit for approval, approval, rejection) functions as well as additional user roles. Editing is a big pro in you can develop templates for not just features but a group of features - a transformer in our design is a series of points for open points / switches, transformer, bus bars etc - the editor can add them as a single entity, and use ArcFM rotation tools to set them cartographically correct quickly. That leads to the Feeder Manager - the biggest pro the utility uses. Open and closing switches or open points well manage the circuits and update values. One gripe about a pro of feeder manager is there is a powerful field of Feeder Information - phased properly, looped, multifeed, de-energized - and it takes some fancy SQL or layer property settings to really harness the power - in ArcFM Desktop - the other products like their OMS make better use of that information, but you can use it in a quality control plan.
More than two cents but in closing it is a very powerful tool but that power does not come without heavy considerations.
